1. Field of the Invention
The invention relates in general to a scanning method, and more particularly, to a method of extracting the position of a transmission document.
2. Related Art of the Invention
In recent years, the improvement in processing speed and data storage for processors and computer related products has greatly enhanced the graphics process. Consequently, image processing equipment such as optical scanners are being improved to comply with the requirement for high resolution and high-speed scan.
Currently, the flatbed scanner is one of the most commonly seen scanners in the market. The flatbed scanner has a document plane such as a glass flatbed for disposing a document or a picture. An optical scan module moving along such document plane is then used to scan the document or picture, so that the image of the document or picture can be extracted. The structure of the flatbed scanner is simple and highly expandable. Therefore, in addition to scanning the typical reflective document or picture, the flatbed applicable to scanning a transparent document or film is broadly used.
The conventional flatbed scanner with transparent scanning function is normally equipped with an external transparency adapter and an external film holder. Referring to FIG. 1, a conventional flatbed scanner with the transparent scanning function is shown. The scanner 100 includes an optical scan module 104, an original document plane 130, an external transparency adapter 120, and an external transparent film holder 110. A transparent document 102 is placed on the original document plane 130, the transparent film holder 110 is located over the original document plane 130, and the transparency adapter 120 over the original document plane 130 covers the scanning region of the transparent document 102. The optical scan module 104 scans the transparent document 102 along the original document plane 130.
Referring to FIG. 1 and FIG. 2 that illustrate the allocation of a transparency adapter for a conventional transparent scan and the transparent film holder, the transparent film holder 110 has a scan window 112, a calibration window 114, and four markers 116. While scanning the transparent document 102, the transparent film holder 110 is disposed on the original document plane 130 of the scanner 100. The transparent document 102 is then placed within the scan window 112. The external transparency adapter 120 is located over the markers 116 to cover both the scan window 112 and the calibration window 114.
In addition, the external transparency adapter 120 projects a plane light source onto the scan window 112 and the calibration window 114. The optical scan module then extracts the light beams transmitting through the scan window 112 and the calibration window 114, so as to discriminate the image of the transparent document 102. The calibration window 114 is used to read the signal of the light source in advance, such that the coverage of the scan window can be properly read.
The conventional transparent film holder provides the scanner the functions of scanning and positioning the transparent document. Once the transparent film holder is missing, the functions of correcting and reading the scan region are lost. The user cannot perform the scanning process for a transparent document anymore.
In addition, the scan window limits the size of the transparent document, and the transparent document has to be disposed within the scan window. This is very inconvenient for the users. Further, the correcting window occupies significant scan area. Therefore, the scanning range cannot be optimized.
Further, the external transparency adapter has to be aligned over the markers of the transparent film holder. Therefore, one cannot arbitrarily change the angle. The external transparency adapter is also an optional device that costs additional expense of the user.